There is a continuous demand for the monitoring of air-borne compounds that may have health effects on exposed individuals. A great interest exists for compounds that have occupational exposure limit values, set by governmental bodies, to ensure that the levels of such compounds are satisfactory low. In many cases it is not known what the air contaminants consist of, and for this reason it is of interest to learn more details about the nature of these “unknown” compounds and to reveal the identity of the most predominate ones. Another field of interest is to study and check the effect of measures with a view to reducing these levels in air, e.g. to check the “true” ventilation efficiency or other measures to control the air levels. Devices for this purpose can also be used for the monitoring of the quality of compressed air and air in respiratory protective devices. Other fields of application for such devices are e.g. the control of different volatile compounds present in food. Such compounds can be used as markers for degradation of certain food components or to monitor raw materials to ensure a satisfactory quality. Such devices may also be used to ensure that other compounds have not contaminated food. In hospitals such devices can be used to check the air levels of e.g. narcosis gases and to ensure that the personnel, patients and others are not exposed to toxic levels. Chemical warfare agents are also compounds that need to be checked for in order to reveal the presence thereof and to ensure that individuals are not exposed.
In environmental analysis there is a need to monitor the quality of air in cities, public places and in the nature or other environments. One purpose is to obtain background data for statistical studies and to check if the levels are below the levels set by national and international bodies. Such devices can also be used to check if the emission of industrial pollutants results in exposure in the nature or in populated areas. The achieved data can have an impact on decisions and interpretation of a certain situation. There is therefore a demand of a satisfactory high quality of the data.
There are many examples of air pollutants that occur in both gas and particle phase. Of special interest are the size fractions that have the ability to reach the lower respiratory tract. There are reasons to believe that the toxicology is different depending on not only the chemistry as such but also on the distribution on different target organs in the body of humans. There is a need to know more about the exposure to the respirable particle fraction present in air. In some cases it is also of interest to determine the identity and amount of inhalable particles, i.e. particles having the ability to pass the nose and the mouth when breathing in, and in some cases the identity and amount of particles that can reach the lungs and lower airways, i.e. particles having the ability to pass through the larynx when breathing in.
Numerous devices exist for the monitoring of air-borne compounds and there is a great variety of technology used. In principle, the devices can be grouped in selective and non-selective devices. Non-selective devices give a response for several compounds and do not differentiate between two or several compounds and may also result in false positive results. Such devices are today still used, possibly due to the low cost. In many applications, false positive results can give rise to a high cost for the user, if costly measures are performed from invalid data.
Selective devices give a certain response for a selected compound or a group of compounds. Other present compounds do not interfere with the result. The frequency of false positive results will be much less as compared to non-selective monitoring. The quality of the data obtained is essential. Typical factors that describe the quality of the data are: repeatability, reproducibility, linearity (calibration graph characteristics with intercept and background), detection limit and quantification limit. In addition, knowledge regarding the interference from other compounds is necessary. It needs to be mentioned that a certain compound can influence the result even if the compound does not itself give rise to a response.
Similar techniques for the detection of air-borne compounds involves the use of e.g. photo ionisation detectors (PID, Thermo Scientific, Franklin, Mass., USA), flame ionisation detectors (FID, Thermo Scientific, Franklin, Mass., USA), infrared detectors (IR), portable gas chromatography (GC)-PID (PID Analyzers, Pembroke Mass., USA), portable GC-mass spectrometers (MS, Inficon Inc., New York, USA), GC-DMS ((Differential Mobility Spectrometry), Sionex Inc., Bedford, Mass., USA). All techniques give a response for a certain analyte, but to know the concentration the response needs to be translated into concentration by using information from a more or less sophisticated calibration curve. For many of the above techniques, the response varies with time due to ageing, contamination of the detector (reduces the signal) and other variables.
The GC-DMS technique mentioned above is used in the MicroAnalyser instrument (Sionex Inc., Bedford, Mass., USA). The GC-DMS technique is based on GC separation, with regards to compound volatility, in combination with the separation in a DMS sensor, with regards to other molecular properties such as size shape, charge etc.
There are several drawbacks with the present types of instruments. For PID and FID, identification of the individual chemicals is not possible. PID and FID detectors measure the sum of VOC (Volatile Organic Compounds). Infrared detectors suffer from problems with inferences. IR detectors are not possible to use when monitoring VOCs at low concentration when other interfering compounds are present.
Polyurethane (PUR) products as air pollutants are of particular interest to monitor and analyze. They frequently occur in industry, in particular in manufacturing and handling polyurethane foam, elastomers, adhesives and lacquers. Polyurethane is produced by the reaction of a bifunctional isocyanate with a polyfunctional alcohol. The satisfactory technical qualities of polyurethane have resulted in a large increase of its use and application fields during the last decades. In connection with thermal decomposition of polyurethanes, however, the formation of isocyanates, aminoisocyanates, anhydrides, and amines might occur, and extremely high contents can be found in air, e.g. when welding automobile sheet steel. Besides the known types of isocyanate, also new types of aliphatic isocyanates have been detected, in connection with e.g. heat treatment of car paint. Most of the isocyanates formed have been found to be represented by so-called low-molecular isocyanates. During short periods of time (peak exposure) particularly high isocyanate contents can be present, as is the case, for instance, when welding. Of all the dangerous substances on the limit value list, isocyanates have the lowest permissible contents. Exposure to this new type of isocyanates was previously unheard of. Isocyanates in both gas and particle phase have been detected in connection with welding, grinding and cutting of painted automobile sheet steel, and particles that can reach the lungs and lower airways in high contents containing isocyanates have been detected. In thermal decomposition products of painted automobile sheet steel, detection has been made of, among other things, methyl isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC), phenyl isocyanate (Phi), 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 2,4- and 2,6-diisocyanate toluene (TDI) and 4,4-methylene diphenyl-diisocyanate (MDI).
In thermal decomposition of phenol/formaldehyde/urea-(FFU)-plastic, isocyanic acid and methyl isocyanate are formed. FFU plastic is used, among other things, in wood glue and as a binder in mineral wool (and bakelite), which is frequently used as insulation for ovens and furnaces in industrial and domestic use. New fields of application in which exposure to isocyanates has been detected are the soldering and processing of printed circuit boards in the electronic industry, the welding, grinding and cutting of painted sheet steel in the automobile industry and the welding of lacquered copper pipes. Isocyanates have a varying degree of toxicity to the organism depending on their chemical and physical form. As a result, the hygienic limit values have been set at an extremely low level in all countries. For the exposed individual, the degree of exposure to isocyanates varies considerably in different operations during a working day and in connection with breakdowns. Thermal decomposition products from PUR constitute a special problem, since new and completely unknown isocyanates are formed, whose toxicity has not yet been analyzed in a satisfactory manner. Furthermore, the increasingly sophisticated measuring methods have revealed exposure to isocyanates in an increasing number of operations in industry.
To sum up, there are a number of operations in numerous working areas where people are daily exposed to or at risk being exposed to isocyanates at a varying degree. Considering the ominous tendency of isocyanates to cause respiratory diseases and the fact that there are some carcinogenic substances among the thermal decomposition products of polyurethane, e.g. 2,4-diamine toluene (TDA), 4,4-methylenediamine (MDA) and MOCA, it is very important to measure in a reliable, sensitive and rapid manner any presence of isocyanates, but also other decomposition products dangerous to health, in environments where there is such a risk.
There is also a particular interest to monitor and analyze such solid/liquid air pollutants as, bacteria, oil mist components, allergens and fungi gaseous organic compounds to analyze are benzene, inorganic gases, volatile organic compounds, chemical warfare agents, anesthetic agents, isocyanates, isocyanic acid (ICA) methyl-isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC), phenyl isocyanate (Phi), 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 2,4- and 2,6-diisocyanate toluene (TDI) and 4,4-methylene diphenyldiisocyanate (MDI), asbestos, dust and metals.
There is also a need to monitor and analyse certain chemical substances present in liquids, e.g. drinking-water, and flows in connection with purification plants. In such cases the liquid flow is transported through a sampling device in which the chemical to analyze is adhered to a specific reagent immobilized within the sampling device, e.g. in a filter and/or on the inner walls thereof, as well as in clean water, waste water, and food.
A sampling device for analysis of air pollutants, more precisely poluretane products, is disclosed in WO 00/75622, and further developments thereof are disclosed in WO 2007/129965, WO 2011/108981, and in WO 2014/193302. The sampling devices, also called samplers, disclosed in these publications collect the probed chemical in a two-step process. A fluid, i.e. a gas or a liquid, in which the amount of a chemical is to be measured, is pumped through the sampling device using a controlled flow. The chemical substance of interest present in the gas phase of the fluid is collected in an adsorption tube using a reagent coated on the surfaces present inside the tube. The flow of fluid is further pumped from the adsorption tube to and through a filter impregnated with the same reagent. The chemical substance in solid form or adhered to particles in the fluid is collected in the filter. After the measurements have been performed, the sampling device is sealed and is shipped to a laboratory for analysis of the amounts of chemical substance collected during the measurements.
It is known to use zeolites in adsorbent tubes, e.g. up to two long steel pipes, for capturing gas phase analytes in fluid flows, but these are not problems with the absorptive capacity.
It is also known that the inner walls of sampling tubes, also called denuders, which may be defined as any devices used to separate a gas from an aerosol, of sampling devices may be coated with carbon particles having the ability to collect and absorb gas phase components, e.g. benzene, in the sampled air flow.
It is also known to provide one or more different reagents on the surfaces of the carbon particles, said reagents having the ability to specifically react with the gas phase components. Sampling tubes which are completely filled or packed with absorbent particles, e.g. carbon particles, for the above-mentioned purpose are also known, also where the surfaces of the sorbent particles are provided with reagents. In such sampling tubes the gas phase compounds bound to the surfaces of absorbent particles or reacted with the reagents provided on the surfaces of the absorbent particles, are then released for subsequent analysis steps via thermal desorption.
The shortcomings and drawbacks with these kinds of known sampling devices are that gas phase compounds are bound to the sorbent, or the reagent provided on the sorbent, with a non-optimal specificity. Up to 90% of the gas phase components in a fluid flow should be captured, but this is not the case with most sampling devices presently used.
Another problem is that water present in the fluid flow to analyze is accumulated or captured as moisture inside the adsorbent tube or denuder, which then creates problems with the sampling capacity. Further, most sampling devices of this kind are difficult to manufacture in a reproducible way, and they are also relatively fragile to handle.
There is also an interest in providing a method of determining the identity and content of respirable and/or inhalable particles in a specific fluid flow, in particular a fluid flow comprising oil mist or vapor, in a more accurate way than so far known. Presently used methods for such a particle exposure assessment are not accurate enough for determining the amount and identity of respirable and/or inhalable particles due to the fact that the particle fraction and the gas phase fraction occur in the same air volume as they cannot distinguish between the two fractions. Further, when collecting particles there may be further release of volatile components from the trapped particles and this will result in the underestimating on the total air borne particles. Further, the pressure drop of the denuder sampler is much less as compared to the sampling in packed beds of particles.
Thus, there is need of an improved sampling method and sampling device for determining the identity and the amount of respirable particles in a fluid flow, and for determining the identity and amount of specific hazardous or otherwise undesired substances in a fluid flow.